DESCRIPTION: (Applicant's Abstract) Marijuana is a widely abused psychoactive substance, however, certain aspects of its pharmacology have the potential for medicinal applications. The cannabinoid, delta-9-tetrahydrocannabinol (delta9-THC), is the principal active constituent of marijuana. It produces a multiplicity of central and peripheral effects including euphoria, analgesia, and immunomodulation. Cannabinoid effects have been attributed to interactions with the G-protein coupled receptors denoted CB1 and CB2. The cannabinoid ligand, WIN 55,212-2, enhances the activity of G-protein coupled inwardly rectifying potassium channels (GIRK1 and GIRK4 or GIRK1/4) when the channels are co-expressed with human brain cannabinoid receptor (CB1) in Xenopus oocytes (X. oocytes). The current proposal will first focus on evaluating the activities of cannabinoid ligands in a X. oocyte system co-expressing the CB1 receptor and GIRK1/4 channels. The CB2 receptor has not been as thoroughly studied as CB1 due to the lack of CB2 in vitro and in vivo assays. Next the activities of cannabinoid ligands will be compared in a X. oocyte system co-expressing the CB2 receptor and GIRKI/4 channels. Alterations of amino acids in receptor proteins by site directed mutagenesis has proven to be an effective method with which to map regions that are important for normal receptor function. X. oocytes expressing mutant cannabinoid receptor constructs and GIRK1/4 will be used to determine which CB1 and CB2 receptor domains are involved in ligand recognition and signal transduction. These studies will increase our knowledge of the nature of cannabinoid ligand-receptor interaction and broaden our understanding of cannabinoid receptor influence on GIRK channels. This information may help to promote the development of more specific therapeutic agents and advance our understanding of marijuana as a drug of abuse.